Screen pipe with fragile lining



Dec. v10, 1940. c. J. DEAN Yx-:TAL

SCREEN PIPEk WITH FRAGILE LINING Filed Sept. 11, 1959 FIG.

`C. J. DEAN F. B. CARTER ORS MAM?

A TTORNEV Patented Dec. '10, 1940 PATENT. IOFFICE SCREEN PIPE WITH FRAGILE LINmG Calvin J Dean, Long Beach, and Frank B. Carter, Glendale, Calif., assignors to Socony-Vacuum Oil Company,ncorporated, New York, N. Y., a corporation of New York Application September 11, 1939, Serial No. 294,266

3 Claims.

It is common practice to nish oil and Water wells by placing a pack or lling of ne gravel between the perforated liner or screen pipe and the Wall of the well within the producing formation. In this practice it is conventional to suspend the gravel in a stream of drilling mud which is pumped down through the casing and returns to the surface through the drill pipe. The screens used for this purpose are lined with a thin layer of cement, which may be drilled out after the job is completed, this cement layer closing all but the lowest perforations and forcing the circulating mud to the bottom of the hole Where the gravel is deposited and accumulates outside the screen until a sufficiently deep annular body has been built up. The purpose in using the cement lining is to enable the operator to apply sufficient fluid pressure to the gravel bed to consolidate it and avoid shrinkage and consequent channeling when the pack is put to its intended use of filtering sandV out of the fluid product and preventing choking of the perforations.

Owing to the ne mesh of the gravel useful for this purpose (which may for example be such as passes a screen of eight meshes to the lineal` inch and is retained on a ten mesh screen) and to the fairly high viscosity of the circulating fluid best adapted to this service, the back pressure due toV the resistance to ow of the constantly increasing depth of gravel becomes very high before the entire bed is in place and is likely to become prohibitive.

We have discovered that this difficulty may be obviated by providing the screen pipe with an internal shell of relatively fragile material such as sand concrete, neat cement, or plaster of Paris so adjusted in thickness and strength as to collapse and thus relieve the external fluid pressure into the pipe When a predetermined optimum iiuid pressure has been reached. In a modification of the invention the lining shell is graduated in thickness so as first to break away adjacent the lower end of the screen and progressively upwardly as higher differential pressures are reached.

The invention may best be understood with reference to the attached drawingfin which Fig. 1 illustrates in a diagrammatic manner the usual arrangement of the parts; Fig. 2 is a section of a liner with internal shell of uniform relatively slight thickness, while Fig. 3 illustrates a liner having a downwardly tapering section.

Referring first to Fig. l, I is an earth bore or well which passes through an oil producing formation Il and has an outer casing or "water string I2 cemented at I3 into an impervious stratum I4 above the producing sand. A liner I5 is placed Within the water string vand is landed or cemented at I6. The lower portion of the liner is perforated as at I8 to form the screen and this portion is again lined with a relatively thin layer I9 of relatively fragile solid material such as concrete, the lowermost perforations being left open as at 20. The drill pipe 2I is run inside the liner and is packed to it as at 22, above the upper end of the screen.

'I'he circulating fluid carrying gravel in suspension is introduced under pressure to the space `between the Water string I2 and the liner I5, at the upper end of the hole. The means for mixing gravel with the fluid and introducing the fluid into this space are conventional and are not illustrated. The suspension ows downwardly, as indicated by the arrows, deposits its burden of gravel on the bottom of the hole as at 23 and returns to the surface through drill pipe 2l.

Referring now to Fig. 2, which is an enlargement of the lower portion of screen I8, the ce-` ment lining I9 covers all but the lowermost of the perforations 20, leaving these open for the return of circulating fluid to the interior of this pipe. The lining is shown as of the same thickness throughout its length, and this thickness is so adjusted, considering the strength of the particular cement paste used in forming it, that the lining will collapse before a pressure is reached which is excessive for the particular well in whichlthe gravel is to be placed. This maximum pressure will vary from Well to well over a very wide range and the thickness of the lining must be varied accordingly.

In Fig. 3 the lining shell I9 is shown as thicker at its upper than at its lower end. This progressive thickening, which causes the lining shell to collapse in stages as the gravel builds up outside the screen pipe may be a gradual taper, as shown at I9a on the left side of the gure, or a stepped thickening as indicated at I9b on the right side. The relative thickness of these 1inings is much exaggerated in the figures.

The fragile linings above described may be cast or spun into place, care being taken to avoid the passage of the paste into the perforations, from which it would be dislodged with difficulty. The perforations may be filled with a fusible material such as asphalt or paraffin prior to applying the lining, or the innerv surface of the screen may be covered with paper for the same purpose. It is desirable to prevent any strong adhesion oi' the lining to the metal of the screen, in order that when it collapses it may break away clean, an end which is served by the paper lining or which may be accomplished by lightly greasing the interior of the pipe before the fragile lining is applied.

We claim as our invention:

1. For use in gravelling wells by a method which includes forcing a mixture of gravel and a. liquid Vehicle down a Well; a screen pipe provided with a substantially nonadherent and relatively fragile lining of a solidsubstance insoluble in said liquid vehicle, the strength of said lining being so adjusted that said lining will collapse, at least in part, under an externally applied pressure less than the maximum pressure tolerable in the well in which said screen pipe is used.

2. A screen pipe substantially as and for the purpose set forth in claim 1, in which the thickness of the lining is less at the lower end than at the upper end of said screen pipe.

3. A screen pipe substantially as and for the purpose set forth in claim 1, in which the thickness of the lining increases by steps progressively from the lower to the upper end of said screen pipe.

CALVIN J. DEAN. FRANK B. CARTER. 

